Furnace



March 8, 1938.

E. o. ENGELS FURNACE Filed Oct. 13, 1954 gwuentoz EUGENE OSCAR ENGELS Patented M... s, 1938 Eugene ,Oscar Engels, Saginaw, Mich., assignor to Baker Perkins Company, Inc.,' Saginaw, Mich, a corporation of New York Application October 13, 1934, Serial No. 748,190 3 Claims. (Cl. 1581) This invention relates to furnaces for heating bake ovens, dry kilns, or the like by the circulation of hot products of combustion through the oven, either through radiating fiues, or by mixing them directly with the'atmosphere of the oven. It has to do more particularly with oil or gas-fired furnaces consisting of a cylindrical tunnel having a burner at one end and opening at the other end into a tubular jacket which encloses it, through which jacket the gases to be heated are drawn or forced at high velocity. V

In furnaces of this kind, especially when used in systems which recirculate spent heating gases from the oven over the combustion chamber where they are mixed with fresh products of combustion, it has been very difficult to provide a material for the combustion chamber walls which will withstand. the extremely high operating temperatures. The'costliest stainless steel cylinders lined with refractory material have lasted only a short time in regular service.

The object of this invention is to provide means for cooling and protecting the combustion chamber walls against intense heat of the gas or oil flame within it, so that longer life will be assured for the structure and its cost of construction and maintenance will be reduced. The invention ac .complishes this purpose by providing novel means at the cylinder end of the-cylindrical combustion chamber for injecting into the combustion cham ber a rapidly moving helically-directed layer of relatively cool inert gases. These gases form a moving blanket over the inner wall of the cylindrical combustion chamber, cooling the wall by convection and preventing erosion by contact with the burner flame.

A further feature of the invention is that the helically flowing layer of gases by its vortex effect produces, or greatly increases, suction at the fuel burnernozzle. This greatly improves the eiliciency of combustion and aids in a certain automatic regulation of fuel and air supply, which will be described further in this specification.

The invention by which these objects are attained resides in the provision of a plurality of openings spaced circumferentially of the combustion chamber wall near the end at which the burner is located,.together with means for directing inert gases such as recirculated flue gases to be heated at high velocity circumferentially of the combustion chamber. A portion of the inert, relatively cool gases enters the combustion chamber at high enough velocity to form a circumferentially rotating blanket of inert gases which sweeps the wall of the combustion chamber or tunnel throughout its length, and surrounds and encloses the burner flame, thus effectively cooling and protecting the tunnel wall or its refractory lining from direct contact with the burner flame. 4

A further feature of the invention may consist of means for positively directing the jets of air entering the combustion chamber so that the flow of inert gases is given a definite helical travel toward the discharge end of the chamber. Ordinarily, however, due to the suction usually present in the chamber, produced either by positive suction of the circulating fan, or by the entrainment effect of gases passing its outlet at high speed, the inert insulating gases while whirling circumferentially of the combustion chamber as The heating plant, shown in Fig. 1, comprises I a tubular jacket or furnace shell I which opens into a heated duct 2 which in turn leads to the inside of an oven or kiln 3'. The hot gases from duct 2 pass either directly into the oven atmosphere, or through radiating flues 4 shown in dotted lines, and thence into an exhaust duct 5. Duct 5 leads to a centrifugal blower 6 which discharges through a duct 1 back into the jacket I at its closed en This known structure forms a closed circuit for the hot gases of combustion, through which they circulate, giving up their heat in the oven 3 and being continuously reheated in the jacket I. So much of the gases as is displaced by fresh products of combustion is vented off through a damper regulated flue Ia leading to a suitable stack or other outlet to the atmosphere.

To the above described structure my invention is applied.

A cylindrical combustion chamber 8, open at one end is mounted coaxially within and spaced from the jacket I. At the burner end the jacket I has a spiral portion la progressively increasing in radius and tapering in width to the point of connectionwith duct 1. The tangentially directed duct is thus faired smoothly into the cylindrical body of the jacket, and portion la defines a spirally tapered duct surrounding the combustion chamber at the burner end. The" combustion chamber may or may not be lined with refractory material 9, depending upon the temperatures which are to be encountered in particular installations.

. Spaced circumferentially of the closed end of the combustion chamber 8 in the outer wall thereof are a plurality of ports or openings [0. The inlet duct 1 is offset, as shown in Fig. 2, so that the gases driven by the blower 6 enter the shell tangentially and are given a rapid travel circumferrentiaily of the chamber past the ports l0. Jets of gas'enter the combustion chamber 8 *thr'dfiah ports III at high velocity and swirl rapidly circumferentially of the interior of the combustion chamber. Due to suction produced by the induction effect of gas passing the open end of the combustion tunnel, the layer of swirling gases travels helically lengthwise along the inner walls of the combustion chamber. As shown in Fig. 1, the gases may be further positively directed in the desired helical path toward the mouth of -chamber 8 by beveling the refractory lining 9 where it is cut away adjacent to ports Ill.

At the closed inlet end of the tunnel 8 a fuel burner l I of known type, to burn premixed air and gas or oil, is installed to direct its flame lengthwise of the tunnel toward its open end.

Heretofore in furnaces of this general type a. great deal of trouble has been caused by the extremely high temperatures to .which the combustion chamber walls were subjected. Expensive alloy steels lasted only a short time under the extreme conditions, and the best refractory hning speedily disintegrated. This invention eliminates that difficulty and permits of the construction of the furnace from relatively inexpensive materials.

In operation, the inert, relatively cool recirculated gases of combustion are supplied at high velocity from duct 1, are given a rapid movement circumferentially of the outside of the cylindrical combustion chamber. Due to their circular travel and relatively high pressure a portion of them flow tangentially into the combustion chamber through ports l0, being so directed by the progressively reduced diameter of the spiral portion la of the jacket enveloping the combustion chamber. Here by reason of their high speed, they form a helically rotating layer of gas, wiping and cooling the inner wall of the combustion tunnel and enclosing as in a tube of gas the axially directed burner flame. In addition to cooling the wall by convection the tubular layer of inert or incombustible gases also protects the wall from oxidation or reduction by direct contact with the burner flame.

A furtheradvantage of my invention in a furnace as shown is that it facilitates the use of a small atmospheric type fuel burner, eliminating expensive and complicated pressure regulating devices for the fuel or combustion air.

In a recirculating system as shown it is desirable to use an atmospheric burner for the further reason that suction at the outlet of the combustion chamber and the entraining effect of the circulated gases varies inversely with their temperature. Thus, with a relatively small flame a high degree of automatic heat regulation is obtained. For example, when the heating gases are cooled below the desired temperature, their density increases. The suction'in the combustion chamber immediately increases, and additional fuel and air are drawn into the burner to in-- crease the rate of combustion.

My invention enhances this eifect by greatly increasing the suction normally prevailing within the combustion chamber around the burner nozzle, and increasing its range of variation with changes of temperature and density of the circulating gases. This increase in suction is brought about by the vortex effect of the layer of gases swirling at high velocity circumferentially of the chamber wall.

- While I have shown my improved apparatusapplied to a recirculating oven-heating system, it p is not limited to such application. For example, it may be used in heating systems for drykilns,

. drying tunnels, etc., in which the spent gases are not recirculated, but are discharged directly to a stack. In such an installation sufiicient relatively cool inert gases may be bypassed from the stack to the blower 6 to produce the desired cooling and protection'of the wall of the combustion tunnel. This, and other modifications in the use of the apparatus embodying my invention may be made without departing from the scope of the appended claims.

' From the foregoing, it will be seen that in the operation of my device the burner flame made of a combustible mixture of air and gas or oil is blown axially lengthwise of the combustion chamber or tunnel B. and that the burner flame is surrounded by an annular layer of burnt, spent, or inert gases, indicated at i2, in the form of a helically swirling fllm or layer that follows around the inner wall of the combustion chamber from the ports ill to the end of the chamber. The burner flame is separated from the inner wall of .the chamber by this protective gaseous layer. Due to the high rate of travel of the layer the inner wall, or the inner lining, of the combustion chamber is protected from the deteriorating effect of the high temperature burner flame, and

consequently the life of the combustion chamber is greatly increased.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In a furnace, in combination, a cylindrical combustion chamber open at one end, a fuel burner mounted in its other end directed axially of said chamber, and a jacket surrounding said chamber and spaced therefrom, a source of inert gases, a conduit connecting said source of inert gases and said jacket, means for impelling gases from said source at high velocity therethrough,

said conduit joined to said jacket adjacent the burner end thereof and directed tangentially of said combustion chamber to direct said inert I maximum radius at said connection and at its minimum radius merging into the cylindrical wall of said jacket to define a gas passage encircling the cylindrical combustion chamber in which the clearance between the said spiral wall portion and the outer wall of said combustion chamber is progressively reduced circumferentially of said chamber.

3. In a furnace, in combination, a cylindrical combustion chamber open at one end and a fuel burner mounted in the other end directed axially v of said chamber, the peripheral wall of said combustion chamber adjacent the burner end being provided with openings therethrough, a source of inert gases, conduit means leading from 

